Flat spot resistant pneumatic tire



FLAT SPOT (|'(0 F), MILS Nov. 30, 1965 Filed Oct. 14, 1965 FLAT SPOT RESISTANT PNEUMATIC TIRE 2 Sheets-Sheet 1 FIG.

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\ uoom. LOAD) D EFGHI EXERCISE a HEATING HISTORY INVENTOR LAVERN JAMES AHLES BY MAEWW ATTORNEY N 0, 1965 .1. AHLES FLAT SPOT RESISTANT PNEUMATIC TIRE 2 Sheets-Sheet 2 Filed 001;. 14, 1963 Y 2:: 352 :55; 25:; $353 M Q o 3 3 I l S'IIIBSNVHO lOdS IV'H c In I o (O I INVENTOR LAVERN JAMES AHLES BY Maw ATTORNEY United States Patent 3,220,456 FLAT SPOT RESISTANT PNEUMATIC TIRE Lavern James Ahles, Meadowood, Newark, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware Filed Oct. 14, 1963, Ser. No. 316,029 12 Claims. (Cl. 152330) This invention relates generally to pneumatic tires and, more particularly, to a nylon-reinforced tire with substantially reduced flat-spotting properties.

Nylon tire cords owe their wide-spread acceptance to the superior service they give under heavy loads, at high speeds, and to their bruise and impact resistance. However, tires reinforced with conventional nylon cords, for example, polyhexamethylene adipamide, exhibit a temporary phenomenon known as flat spotting, i.e. a flatness develops on the tire surface in contact with the road as the tire stands still and cools after use. When the tire is again placed in use, this flatness persists temporarily and a thumping sound is audible. This phenomenon has been attributed at least in part to such visco-elastic properties as the relatively low dimensional stability, low modulus, and high growth of conventional polyamide yarns.

An object of the present invention is to provide a nylon-reinforced tire which does not flat spot even after prolonged storage.

Another object is to provide a process for treating a tire having nylon cords in the carcass to reduce flat spotting tendencies.

These and other objects will become apparent in the course of the following specification and claims.

In accordance with the present invention a process is provided which comprises contacting the hollow chamber presented by a pneumatic tire casing with a desiccant and sealing the said hollow chamber containing the said desicca-nt. The process provides an article of commerce comprising a pneumatic tire casing presenting a hollow chamber, means to seal the said chamber and desiccant means within the said chamber to provide an atmosphere of low moisture content.

The invention will be more readily understood by reference to the drawings. FIGURE I is a series of curves wherein flat spotting measured in mils at 170 F. as ordinate is plotted against a series of consecutive cycles of exercise and heating as abscissa, the points A, B, C, D, F, G, H, and I representing two hours exercising at 70 mph. under the loads indicated followed by two hours heating at 190 F. (point E representing eight hours exercising and two hours heating under the same conditions). FIGURE II is a series of curves wherein the reduction in flat spotting in mils is plotted as ordinate against the same abscissa as in FIGURE I.

The following examples are cited to illustrate the invention. They are not intended to limit it in any manner. Where flat-spot depth is reported, the value is obtained by measuring with an Ames gauge the unloaded out-ofroundness in mils of a tire heated to 170 F. Then the heated tire is loaded against a flat surface with 90% of the maximum permissible load specified in the 1962 Yearbook of the Tire and Rim Association, 2001 First National Tower, Akron 8, Ohio, and allowed to cool for two hours. The out-of-roundness is measured again and corrected for the over-all shrinkage of the tire. The difference between the two values is the flat-spot depth. In actual practice, riding characteristics are acceptable with a flat-spot depth of less than 160 mils. depth does not exceed 140 mils.

EXAMPLES 1-9 In each of Examples 1 to 9 the tire as identified in Table I is mounted on a tire rim and is inflated to 22 p.s.i.g. pressure. Where a desiccant is employed it is placed in the air cavity of the tire prior to mounting. Where the desiccant is solid it is attached in cheesecloth bags equally distributed around the rim. All the tires used in these examples are tubeless pneumatic tires having a bias carcass. The nature of the cord in each tire is indicated by code in Table I, the code designation being identified in Table II. The results are plotted in the curves of FIGURES I and II, the curves relating to each tire being identified in Table I. The improvement obtained following the process of the present invention is obvious from an inspection of the curves.

Preferably this Table 1 Ex. Curve Tire 00rd l Desiccant 1.. A 4ply,8.5014 G6/GtI (EEO/20)..-. None. 2 A1 4 ply, 8.5014 66/6tI (/20) 1 lbfimhy. ealc.

su 3 B 2 ply, 800-14.--- 66/61 (80/20)..- None. 4 B 2 ply, 800-14.-" 66/61 (80/20) 1 lbfitnhy. calc.

su 5 C 2 ply, 7.50l4 66/61 (80/20)- None. 6 C 2 ply, 7.5014 66/6I (80/20) 1 lb. silica gel. 7 C 2 ply, 750-14-.-- 66/61 (80/20) 1lb.l:f1nhy. calc.

su 8. C 2 ply, 750-14-." 66/6I (80/20) 1 p111. diethyleneg yco 9 0.1 2 1 7.50-14 66/61 (80/20) 1 pt. tetraethyleneglycol.

1 Figure in parenthesis indicates parts by weight of melt blend of the indicated components.

Table 11 Code Symbol Polymer Identity Polyhexamethylene adipamide.

Polyhexamethylene isophthalamide.

EXAMPLE 10 This example illustrates the observation that the flat spotting tendency of a nylon cord tire tends to increase upon storage of the tire unless treated in accordance with the process of the present invention. In this example a four-ply, bias-carcass, tubeless pneumatic tire of size 8.50-14, reinforced with relatively dry cords fabricated (under conditions of less than 20% relative humidity) with filaments spun from an 80/20 blend by weight of polyhexamethylene adipamide/polyhexamethylene isophthalamide is determined to have a flat spot of 128 mils. After unmounted storage for days at 90 F. and 80% relative humidity, it has a flat spot of 165 mils. Two pounds of highly porous, granular structured, anhydrous calcium sulfate is poured into the air cavity of the tire, it is mounted on a tire rim, inflated to 22 p.s.i.g. pressure and exercised by rotation at 65 mph. for 1500 miles against a smooth surface with the tire carrying a load of 1085 pounds. Thereafter the tire has a flat spot of mils. A comparative control tire of the same construction with an initial flat spot of 128 mils has a flat spot of 163 mils after the unmounted storage period. After mounting, inflating and exercising in the manner of the Polyhexamethylene t-butyl isophthalamide.

"illustrative embodiment, without the calcium sulfate, the

control tire has a fiat spot of 157. The tires are then stored mounted for the period of days noted in Table III. Periodic flat spot determinations are made with results Example 10, two pounds of anhydrous calcium sulfate (approximate volume 60 cu. in.) occupies about 2.4% of the volume of the hollow chamber (approximate volume 2550 cu. in.) presented by a 850-14 tubeless tire inflated presented in the table. Before each determination the 5 to 22 p.s.i.g. tires are exercised about 1 /2 hours. Table I V b e 1 Unprocessed Processed Tire, percent Tire. percent Days Storage g s Conml 1O Cord 1.5 Skim 0.3 0.1

- 123 163 i? While applicant does not wish to be bound by any 40 114 172 theory, it appears that tendency to flat spot is related to m 176 the moisture content of the cord.

In addition to tires containing those cordsdspecififally illustrated above, tires containing cords pro uced rom EXAMPLE 11 poly-caproamide may be employed. Any desiccant, This example illustrates the retention of resistance to whether liquid, solid or gaseous is suitable. When the flat spotting of a tire treated in accordance with the presdesiccant becomes saturated with moisture it may be reent invention under conditions of actual use. In this placed with a new desiccant. The desiccant may be example a four-ply, bias-carcass, tubeless pneumatic tire placed in the tire cavity either separate or along with the of size 7.5014 reinforced with cords fabricated (under air that inflates the tire. conditions of high relative humidity) with filaments spun The preferred process for providing apneumatrc tire from polyhexamethylene adipamide is determined to have with low flat spot according to this invention is heating a a flat spot of 208 mils. One pound of highly porous, mounted tire with a desiccant in the tire cavity. Some granular structured, anhydrous calcium sulfate is placed reduction in flat spot may be attained by storing the in the air cavity and the tire is mounted on a tire rim, inmounted tire at room temperature, but at very low relaflated to 22 p.s.i.g. pressure, and thereafter placed in an tive humidity, with the desiccant in the tire cavity. Exoven at 190 F. for 36 hours. The tire then has a flat ercising and/or heating tires with desiccant 1n the air spot of 136 mils. Thereafter the tire is dismounted, the cavity is effective regardless of past storage conditions, anhydrous calcium sulfate is removed and is replaced by and the desiccant in the air cavity can be renewed as 250 milliliters of tetraethylene glycol. This tire is then needed. remounted on its rim and placed into service on a passen- It is apparent that other variations and modifications in ger car for 29 days. At the end of this period the tire the tire, and in the procedures followed, may be adapted has a flat spot of 135 mils. without departing from the spirit of the present invention, EXAMPLE 12 which is therefore intended to be limited only by the scope of the appended claims. A tire of the structure of Example 10, but containing 40 Wh t i laim d i an innerliner of chlorobutyl rubber (a rubber composition 1, A o d r infor ed neumatic tire having reduced which resists passage of air providing a particularly leakfiat-spotting tendencies which comprises cord formed from proof tire) is observed to have a flat spot of 197 mils. a high molecular weight polycarbonamide wherein the One pound of anhydrous calcium sulfate is provided in recurring carbonamide linkages are an integral part of the air cavity. The tire is mounted, inflated and exerthe polymer chain, from the class consisting of (A) cised in accordance with the procedure described in EX- olycaproamide, (B) polyhexamethylene adipamide, (C) amples 1-9. At the end of the cycle the tire is observed a melt blend of (a) polyhexamethylene adipamide and to have a flat spot of 137 mils. Although the process of (b) polyhexamethylene isophthalamide and (D) a melt the present invention is more effective in reducing the blend of (a) polyhexamethylene adipamide and (b) polflat spot of tires whose innerliner do not resist the passage yhexamethylene-t-butyl isophthalamide, the casing of the of air, this example shows that the invention may be adsaid tire presenting a hollow chamber, said hollow chamvantageously used on tires with an air barrier innerliner. her having therein air under pressure together with a rela- EXAMPLE 13 tively small amount in relation to the volume of said hollow chamber of desiccant means, and means to seal the Extended oXPoSuTo to a rolatlvoly hlgh temperature said hollow chamber from contact with the atmosphere. (from about to about of 'fi containing 2. The tire of claim 1 wherein the flat-spot depth does desiccant sealed in its air cavity can be used to greatnotexceed 160 11 ly reduce the flat spotting tendency. To illustrate this 3, Th i of l i 1 h i h id polycarbom two tires of the structure of Examples 5-9, having id i polyhexamethylene di id initial flat spots Of and respectively, 4 The tire of claim 1 wherein the aid polygarbonare mounted, each With oho Pound of anhydrous Calcium amide is a melt blend of polyhexamethylene adipamide sulfate in its air cavity, inflated to 24 p.s.i.g. pressure and and polyhexamethylene isophthalamide. heated for 36 hours The flat Spots of the tires 5. The tire of claim 1 wherein the said polycarbonamide 50 treated are 73 mlls and 84 mils respectively TWO is a melt blend of polyhexamethylene adipamide and other tires of the same construction are dissected to depolyhexamethylene-t-butyl isophthalamide. termine the moisture content of the cord and the skim 6. A cord reinforced pneumatic tire having reduced rubber; o o the dissected o being as received, the fiat-spotting tendencies which comprises cord formed other being dissected after the tire had been subjected to from a high molecular Weight polycarbonamide wherein the heating process described above. The results are rethe recurring carbonamide linkages are an integral part ported in Table IV. As is apparent from the foregoing, of the polymer chain, from the class consisting of (A) the desiccant occupies only a relatively small portion of polycaproamide, (B) polyhexamethylene adipamide, (C) the hollow chamber of the pneumatic tires. For exa melt blend of (a) polyhexamethylene adipamide and ample, in Example 6 one pound of silica gel (approximate (b) polyhexamethylene isophthalamide and (D) a melt volume 10 cu. in.) occupies about 0.47% of the volume blend of (a) polyhexamethylene adipamide and (b) of the hollow chamber (approximately 2100 cu. in.) prepolyhexamethylene-t-butyl isophthalamide, the casing of sented by a 7.50l-4 tubeless t1re inflated to 22 p.s.i.g. In the said tire presenting a hollow chamber, said hollow chamber having therein air under pressure together with from 0.47% to about 2.4% by volume of said hollow chamber of desiccant means, and means to seal the said hollow chamber from contact with the atmosphere.

7. The tire of claim 6 wherein the flat-spot depth does not exceed 160 mils.

8. The tire of claim 6 wherein the said polycarbonamide is polyhexamethylene adipamide.

9. The tire of claim 6 wherein the said polycarbonamide is a melt blend of polyhexamethylene adipamide and polyhexarnethylene isophthalamide.

10. The tire of claim 6 wherein the said polycarbonamide is a melt blend of polyhexamethylene adipamide and polyhexamethylene-t-butyl isophthal amide.

11. A process for reducing fiat-spotting in a cord reinforced pneumatic tire, the said cord being formed from a high molecular weight poly-carbonamide wherein the recurring carbonamide linkages are an integral part of the polymer chain selected from the class consisting of (A) polycaproamide, (B) polyhexamethylene adipamide, (C) a melt blend of (a) polyhexamethylene adipamide and (b) polyhexamethylene isophthalarnide and (D) a melt blend of (a) polyhexamethylene adipamide and (b) polyhexamethylene-t-butyl isophthalamide, the casing of the said tire presenting a hollow chamber substantially filled with air under pressure, said process comprising introducing into the hollow chamber presented by said cas ing a dessiccant which occupies a relatively small amount of the volume of said hollow chamber, and then sealing said hollow chamber.

12. A process for reducing flat-spotting in a cord reinforced pneumatic tire, the said cord being formed from a high molecular weight polycarbonamide wherein the recurring carbonamide linkages are an integral part of the polymer chain selected from the class consisting of (A) polycaproamide, (B) polyhexarnethylene adipamide, (C) a melt blend of (a) polyhexamethylene adipamide and (b) polyhexamethylene isophthalamide and (D) a melt blend of (a) polyhexamethylene adipamide and (b) polyhex-amethylcne-t-butyl isophthalamide, the casing of the said tire presenting a hollow chamber substantially filled With air under pressure, said process comprising introducing into the hollow chamber presented by said casing a desiccant which occupies from about 0.47% to about 24% of the volume of said hollow chamber, and then sealing said hollow chamber.

References Cited by the Examiner UNITED STATES PATENTS 2,109,383 2/1938 Gallardo l 52-330 2,991,818 7/1961 Gay etal 152359X ARTHUR L. LA POINT, Primary Examiner. 

1. A CORD REINFORCED PNEUMATIC TIRE HAVING REDUCED FLAT-SPOTTING TENDENCIES WHICH COMPRISES CORD FORMED FROM A HIGH MOLECULAR WEIGHT POLYCARBONAMIDE WHEREIN THE RECURRING CARBONAMIDE LINKAGES ARE AN INTEGRAL PART OF THE POLYMER CHAIN, FROM THE CLASS CONSISTING OF (A) POLYCAPROAMIDE, (B) POLYHEXAMETHYLENE ADIPAMIDE, (C) A MELT BLEND OF (A) POLYHEXAMETHYLEN ADIPAMIDE AND (B) POLYHEXAMETHYLENE ISOPHTAHLAMIDE AND (D) A MELT BLEND OF (A) POLYHEXAMETHYLENE ADIPAMIDE AND (B) POLYHEXAMETHYLENE-T-BUTYL ISOPHTHALAMIDE, THE CASING OF THE SAID TIRE PRESENTING A HOLLOW CHAMBER, SAID HOLLOW CHAM- 